It's for accredited investors only and illiquid. Investors are essentially making indirect loans to businesses that install solar panels. Apparently, traditional sources of financing won't make these loans.
The large US-based solar companies are struggling mightily due to competition from low oil prices and cheap Chinese solar manufacturers.
I have no idea exactly where Wunder gets its products or who installs and maintains them. It seems like a middleman operation that the banks won't touch.